EETC Electrical Equipment & Maintenance 2

Question 1

What is the primary purpose of a megohmmeter (megger) in electrical maintenance?

Accepted Answer

Test insulation resistance of cables and motors

Answer

A megohmmeter applies high DC voltage to measure insulation resistance, detecting degraded or damaged insulation before failures occur.

Question 2

When performing a polarization index (PI) test on a motor winding, a PI ratio below 1.0 indicates:

Accepted Answer

Severely contaminated or damaged insulation

Answer

A PI ratio below 1.0 means insulation resistance decreased during the test, indicating moisture saturation, contamination, or serious deterioration.

Question 3

Which type of capacitor failure mode causes an electrolytic capacitor to vent or bulge?

Accepted Answer

Excessive ripple current causing internal heating

Answer

Excessive ripple current heats the electrolyte, generating gas pressure that bulges or ruptures the vent on an electrolytic capacitor.

Question 4

In a three-phase induction motor, what condition is indicated by high vibration at twice line frequency (120 Hz in a 60 Hz system)?

Accepted Answer

Loose stator laminations or electromagnetic looseness

Answer

Vibration at 2× line frequency (120 Hz) is a classic signature of electromagnetic looseness, often caused by loose stator core laminations.

Question 5

A transformer's dissolved gas analysis (DGA) shows high levels of acetylene (C₂H₂). What fault does this indicate?

Accepted Answer

High-energy arcing or electrical discharge

Answer

Acetylene is produced only at very high temperatures (above 700°C), making it a definitive marker of high-energy arcing inside the transformer.

(EETC) Electrical Technician Certification Practice Test